113 
ON THE STRUCTURE OF .CAMERATED SHELLS. 
By HENRY WOODWARD, F.G.S., F.Z.S., 
Op the British Museum. 
[PLATE LXXXII.] 
A MONG- the various natural objects which the ingenuity of 
man in all ages has converted into articles of use or orna- 
ment, both in savage and civilised life, none have attracted a 
greater amount of attention, or have been more in request, than 
the shells of Mollusca, especially sea-shells. 
Their bright colours and diversity of form are among their 
chief charms to the uninitiated; whilst, to the student of 
natural history, they offer ample materials for scientific 
research. 
The shell in the Mollusk may be regarded as a calcified por- 
tion of the mantle specially provided (like the enclosing ribs of 
the vertebrata) to afford protection to the breathing organs and 
heart. Indeed, when reduced to a mere rudiment, as in Limax , 
Testacella , Carinaria , &c., it forms only a hollow cone or plate 
protecting these organs. 
This structure, which has sometimes been called a Pneumo- 
skeleton, is so characteristic of the Mollusca as to have 
obtained for them the title of Testacea ,* and the common name 
of “ shell-fish ” very well expresses the leading feature in the 
group. 
Nevertheless, in one whole class, the Tunicata , and in 
several families, the shell is either wanting altogether, or is 
internal, or so rudimentary that it would never be popularly 
recognised as a shell. When fully developed, the shell of the 
Mollusk subserves to protect the soft parts of the animal from 
injury, and the animal itself from the attacks of enemies, and, 
in some of the Gasteropoda , from those variations of tempera- 
ture and moisture to which the terrestrial species are peculiarly 
exposed. 
* From testa, a shell. 
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VOL. XI. — NO. XLIII. 
